Sample For Nematodes 4-6 Weeks After Planting
LEXINGTON, KY.
Nematodes are microscopic
roundworms that
attack roots of corn and
other plants. In corn, nematodes
affect yield by damaging
the root system and interacting
with opportunistic rootrotting
fungi. They become
more important when there
are other root-related stresses in the same field,
such as moisture shortage, root damage from
insects, or compaction.
Although there is increasing interest in nematodes
as potential yield-limiting factors, the
threat these pose varies greatly from one field to
the next. The best way to determine whether
nematodes may be affecting yield is to sample
for nematodes.
When to Sample
The window at 4-6 weeks after planting is
probably the easiest time to sample, since the
nematodes will be in the root zone and the soil
is often moist enough to be able to insert a soil
probe. Plus, sampling early in the growing season
will give an idea as to whether nematodes
are likely to affect crop productivity. Summer
sampling is less than ideal. During summer,
certain nematodes (like the sting nematode and
needle nematode) move downward in the soil,
where the moisture is. Also, pulling samples
from dry soil is difficult. After harvest, sampling
gives a look at certain nematode populations,
especially endoparasites (lance nematode and
root-lesion nematode, which burrow within the
corn root), as well as the nematodes that go
deep into the soil during summer.
How to sample
The most important thing to realize is that
sampling for corn nematodes is different than
sampling for soybean cyst nematode. For corn,
sampling guidelines are as follows:
• Instead of sampling at random, in a zig-zag
pattern, sample parts of the field where yield
losses or symptoms (stunting, yellowing in
elongated areas of the field) are not explained
by other factors, such as soil compaction, soil
type, etc. Corn nematode populations can be
extremely variable (see Figure 1), so focus sampling
on potentially problem areas of the field.
However, for severely affected areas of the field,
sample from the edge of the damaged areas
rather than in the worst areas. (This is because
corn nematodes require live roots to feed on,
and if plants are severely damaged or dead, the
nematode numbers will be low.)
• Make sure to sample within the row–that’s
right, within the row. This is different from
sampling for soil fertility. Take 20-25 samples.
• Sampling for nematodes in corn requires a
depth of at least 12 inches. This is much deeper
than for soybean cyst nematode. If sampling in
summer or fall, one may need to go as deep as
24-36 inches in order to detect sting nematode
or needle nematode (although these two nematodes
are usually found only in sandy soils).
• Put all 20-25 soil cores in a Ziploc bag. Don’t
break the soil cores, since some nematodes like
stubby root nematode are extremely sensitive
to soil disturbance. Label the bag with a permanent
marker (not a magic marker, which
comes off in water). Store samples in a cool,
dry place until shipment.
Where to send samples
Laboratories that can analyze nematodes in
soil samples collected at this time of year include:
• University of Illinois, http://plantclinic.cropsci.illinois.edu/submit.html#nematode
• Purdue University,
http://extension.entm.purdue.edu/nematology/cv/submissionform.pdf
cv/submissionform.pdf
• Mississippi State University,
http://msucares.com/pubs/misc/m1230.pdf
• University of Florida,
http://edis.ifas.ufl.edu/sr011
• Iowa State University, http://www.extension.iastate.edu/Publications/PD32.pdf Δ
DR. PAUL VINCELLI: Extension Plant Pathologist,
University of Kentucky